The present invention relates to the display of serial digital television signals, and more particularly to digital cursors for serial digital television waveform monitors.
Television signals are now being transported as a serial digital signal in accordance with CCIR 601. Current technology uses a scrambled NRZI signal to represent the serial digital signal. The actual values are difficult to determine in this form due to the scrambling. When two pieces of equipment are interconnected and do not function properly, it is necessary to determine if the transmission is correct. Viewtronics Ltd of the United Kingdom has developed a DIGIVIEW measuring system for digital television signals for use with personal computers. A serial input card converts the serial digital signal to a parallel digital signal in accordance with CCIR 656. A DIGIVIEW expansion card accepts the parallel digital signal and displays it in either tabular or graphic form on the computer screen. Another approach is to use a dedicated television signal measurement instrument, such as the WFM601 Serial Component Monitor manufactured by Tektronix, Inc. of Wilsonville, Oreg., United States of America, to display serial digital signals. The serial digital signal is converted to a parallel digital signal, descrambled (or descrambled and then converted) and separated into individual component signals, Y, Pb, Pr. The individual component signals are converted into analog signals and appropriately filtered. The resulting analog signals may then be conventionally displayed on a suitable display device, such as a cathode ray tube, liquid crystal display, or the like. Such a waveform monitor is disclosed in U.S. Pat. No. 5,311,295 issued May 10, 1994 to James L. Tallman et al entitled "RGB Display of a Transcoded Serial Digital Signal", incorporated herein by reference.
To perform measurements on the displayed analog waveform the waveform monitors provide cursors to readout time and voltage values. These may be in the form of variable analog voltage values that are added to the analog waveform. Such cursors are disclosed in U.S. Pat. No. 5,047,709 issued Sep. 10, 1991 to Davorin Fundak entitled "Calibrated Voltage Cursors", incorporated herein by reference. The voltage level of the cursor may be converted to a digital value for display, either in terms of voltage or time.
What is desired is to provide an analogous digital cursor that is inserted into the serial digital signal to provide a direct readout of the cursor values while maintaining accuracy between the cursor and the serial digital signal.